Multiplex telegraphy



June 15 1926.

R; V. L. HARTLEY MULTIPLEX TELEGRAPH! Filed lla rch: 9, 22 2 Sheets-Sheet 1 ha enfon R44? Half/e fit) Patented June 15, 1926. i I

UNITED "STATES RALPH V.'L. HARTLEY, OF EAST 1,588,415 PATENT OFFICE.

ORANGE, NEW JERSEY, ASSIGNOIR- TO WESTERN ELEC- TRIO COMPANY, INCOBPORTED, OF NEW YORK, N. Y., A CORPORATION OF NEW ORK.

Application, filed March 9,

The present invention relates to thetransmission and reception of telegraphic or sim ilar signals by alternating currents or Waves, the conversion from direct-current telegraph impulses to the alternating currents or vice versa being accomplished by commutation.

Telegraph transmission by means of alternating currents or Waves, produced by any of the Well-known Wavegenerators and 0011-. trolled in some manner asby a key or by direct-current impulses have been suggested, and the features of such a system have by this time become generally familiar. One of I the principal advantages of such a system is that the same line may be used to transmit a number of currents of distinct frequencies. which can be independently controlled by diflerent signals and can be separately receivedhy means ofselective circuits, permitting, of multiplex operation. The types of Wave sources or generators heretofore devised andsuitablefor use in such a system are all relatively costly apparatus, and the use, particularly of vacuum discharge tubes which has become quite general in such systems, introduces certain difficulties in trans mi sion which will he referred to more in cletail hereinafter.

One object of the invention is to provide means and method, involving current commutation as stated, for'securing the advanof alternating current, or carrier cur rent as it is commonly called, transmission at less cost of equipment than has been involved in systems heretofore devised;

A further object of the invention is to overcome the diiiieulties experienced in using discharge tubes, as mentioned above, the par ticular features for overcoming these difficulties to be explained in the detailed description to follow; I

The useof commutators for transmission and reception in the manner to be described hereinafter requires that distantly separated cominutators be synchronized. It is common to employ synchronized rotary distributors or the like in printing-telegraph systems. These systems even though they mayoperate four one-Way or four two-Way printing telegraphchannels do not nake use of more than asmall. portion of the total frequency range which the line isgenerally ca-- pahle of transmitting, and it is'a further ol ctof the invention to utilize the range miracl s intes at -Refit ased, b 1

the opposite terminal.

7 be designed in accordance with the Y ciples disclosed in the patent .to G. A. Campbell, No. 1,227,113, issue filter LP to t -by the filter LP, but

MULTIPLEX TELEGRAPHY;

922. Serial No. 542,250.

tion Will appear from the following detailed description "01"- a typical embodiment of the. invention as illustrated in the accompanying drawing, in which Fig. 1 shows a terminal station of a system embodying the inventlon; Fig. 2 shows a somewhat d1ferent arrangement of the circuits at a terminal station; and Fig. 3 shows a modification ot'a channel termination. i I

Fig. 1 shows a terminal station line Ml it being assumed that the for the pposite terminal is arranged identically with the one shown, or diti'ers therefrom only in uncs sential respects. The hne ML is in the pres ent 'instance compesitcd so as to serve for the transmission both of telegraphic im- I pulses and alternating currents having fre quencles higher than the frequencies involved in the telegraph impulses. The telegraph impulses inthe present instance are those employed by the printing telegraph apparatus PT and a corresponding apparatus at rents are employed for repeating be ween The alternating curthe direct current telegraph line LL Ll'f and similar distant'linesbyWay-of the main line ML. The printing telegraph impulses are separated at the terminal from the alternating currents or Waves as a hole by the wave filters LP and HP, These filtersmay prind May 22, 191?. The is a low pass filter and is designed sinit freely all frequencies om Zero tof'a predetermined upper limiting trequency,-

but-to suppress the transmission of currents 10G- The highpass filter HP is d'eigned'to prevent the transmission of curhaving frequencies higher than this limiting frequency. s

rents of the range of frequencies.transmitted freely transmits frequencies higher than this range. A balancin'g network'N is provided foi' matching the characteristics of the 'linecircuit', and in HP in the betwee eluded.between the network and the filter sual three wlnding transformer transmitting loop TL, the receiving loop BL, and the line.

The printing telegraph apparatus PT is controlled, in receiving, by the line. relay LR, and'this apparatus comprises the rotary distributor 20, the receiving recorder or printer 21, and suitable synchronizing apparatus indicated at 22 for driving the shaft 23 at a uniform rate and in synchronism with the distributor shaft. at. the dis tant station. Arrangements for maintaining distributors of this sort in synchronism are well known in the 'art and it is not deemed necessary to show or describe the details of such arrangements for the purposes of the present disclosure- It will be assumed. however, that either the telegraphic signals which actuate the line relaylllt or some special control impulses or currents are transmitted between the station illustrated and the distant station, whereby phase corrections are made in one or both distributors or some other control is exercised to maintain the distributors in step. The circuit 24: is assumed to lead to a suitable printing telegraph 'transi'nitter which may be connected to the line by means of the switch 25 in place of the line relay, if desired.

The alternating current or carrier current channels, as illustrated, comprise the commutators 30, 31, 32 and 33, together with their associated filters. These com.- mutators are indicated as-being driven from common shaft shown in dotted lines and designated as This shaft is assumed to be driven in, any suitable manner from the synchronizing apparatus 22 of the printing telegraph equipmentand in this manner to be maintained in synchronism with a corresponding shaft at the distant station, siniilarly driven from the printing telegraph apparatus at that station, and in turn, driving the commutators employed at that station for the carrier channels. The channels shown comprise two two-way or full duplex telegraph channels, the two channels of the two-way channel cooperating with the duplex line LL including the commutators 30 and 32, and the channels cooperating with the duplex line LL including the commutators 31 and 33. The .commu tater 30, for example, has a pair of its brushes connected by way of the low pass filter LE to the circuit including the contacts of the receiving relay 36 of the line LIB, this circuit alsoi-ncluding a battery. The filter L is designed to pass frequencies from zero up to the highest essential frequency involved in the transmission of telegraphic impulses from the relay 36 and suppresses frequencies higher than these. As is well understood, these essential fre= quencies comprise'not oily the impulse frequen'ey, but; many higher frequencies, due

to the sharp making and breaking of the telegraph circuit to transmit the impulses. The other brushes of the commutator 30 are connected to the common transmitting loop TL by way of the band pass filter TF Each of. the commutators 30 to 33, al-

though indicated as being driven from the same shaft 35, is arranged to operate at a different rate of commutation due to the individual driving connections or to the arrangement of the commutator segments. The commutator 30, for example, may be arranged to operate at a commutating fre quency of 150 cycles per second. If then the low pass filter LE transmits frequencies from Zero to 100 cycles per second, this range being assumed ample to cover all of the es sential frequencies involved in direct-current telegraph transmission, the frequencies resulting from the operation of commutator 30 will include a lower side band having a maximum range from about 50 to 150 cycles and an upper side homologous range 250 cycles. The band pass filter TF 'niay. under theseconditions, be designed to pass frequencies from 150 to 250 cycles but to suppress the transmission of frequencies both lower and higher than the stated range.

The commutator 31 is arranged to have a different frequency of commutation, for example, 300 cycles per second. The filter Ll, hrough which impulses are received from the relay 37 of the line LIE, is assumed to be a duplicate of the filter LE. Of the frequencies resulting from the commutator 31 only the upper side band comprising frequencies from 300 to 400? cycles are transmitted by the band pass filter TF The receiving filter RF may be a duplicate of the filter TF and the commutator 32 may be 'a duplicate of tie commutator 30, both of these being operated rate. Similarly, the receiving filter 333? and the commutator 33 may be duplicates hand comprising a from about 150 cycles to the operation of at the same of the corresponding transmitting elements.

If preferred, however, different frequencies may be used for transmission by the same two-way channel in opposite directions, in which case. the commutators 32 and 33 and the filter R'F and RF to employ other frequencies. The low pass filters LE and LF included between the both side-bands of the respective alternating-current telegraph wave.

would be designed 7 The operation of the system is as follows: The printing telegraph channel including the apparatus VPT ant similar apparatus at the distant station operates in the normal manner and employs frequencies Within the range of zero to 120 cycles or less. Currents of these frequencies are transmitted to the line ML and received from the line ML as required, through the filter Ll but currents of these frequencies are prevented from pass ing into the carrier channel terminals by the high pass filter HP. Currents having frequencies of 150 cycles and higher pass freely through the filter HP, but are prevented from passing into the printing telegraph channel by the filter LP.

Considering now signals originating on the telegraph line LL these signals are received by the relay 36' which actuates its armature to close a circuit including the local battery, the filter LF and a pair of brushes of the commutator 30. This commutator as stated is assumed to have a commutating frequency of 150 cycles and the band pass filter TF to be arranged to pass the upper side band containing frequencies between 150 and 250 cycles. Currents of this range are used exclusively by this channel and are transmitted to the common loop TL and through the three-winding transformer and the filter HP to the main line.

In .a similar manner, relay 37 is actuated by impulses received over the line LL and connects battery to the commutator 31, which produces from the direct current impulses alterna ing currents having frequency components both lower and higher than the carrier frequency of 300 cycles, While the filter TF transmits the upper side band including frequencies between 300 and 400 cycles. These currents are also impressed on the loop TL and the line ML. In a similar manner other channels employing co1ninutators having other frequencies and filters of corresponding frequency rangesmaybe connected with the transmitting loop TL.

The action at the distant receiving station of the currents transmitted to the line ML in the manner described will be clear from considering the action at the terminal illustrated of currents received over the line ML from the distant station. Currents so received having frequencies higher than 150 cycles pass through the filter H? into the common receiving loop RL. Of these currents, those having frequencies within the transmission range of the filter R'F pass through this filter to a'pair of brushes on the commutator 32. It is assumed that this commutator is a duplicate of the commutator and that a duplicate pair of commutators are eni-' ployed at the opposite terminal station, one for transmitting and the other for receiving and further that these commutators are all operated in synchronism. Under these conreceived causing relay39 to actuate its armature andbattery shown having ditions, the filter LF and the relay 39 receive direct-current impulses produced by rectification by the commutator 32 from the alternating-current Wave trains,

to transmit current from the to the duplex line LL filter LE serves to smooth out the direct-current im ulses by suppressing the high frequency components caused by interruptions or irregularities of operation in thecoinmututo'r In similar manner the filter EF passes currents having another frequency range and the coininutat'or 33 converts the received alternat ing currents into direct-current impulses for operating relay 4-0 to repeat into the line LL The method of modulation by means of a commutator as above described has ceta-in advantages over the useof the familiar vacuum tube for modulation. The principal advantage of the commutator in the system par icularly described herein is that itproducesfroir. the applied direct-current impulses the two side frequencies or side bands that are produced by any modulator, but it does not produce certain other frequency components which are found troublesome in the use of vacuum tube modulators. lVith the arrangements shown herewith in Which a direct-current component is applied to the commutator brushes an alternating current of the carrier frequency is also pro-- duced in addition to the two side bands and due to sharp interruptions and to unavoidable irregularities in the commutator, there will be a number of frequencies produced all of Which are bi h in comparison With thecarrier and side band frequencies. These can easily be suppressed by the use of a filter a limited transmission range. The

commutator does not, however, produce the harmonic frequencies of the applied waves that are .to be found in the output of a vacuum tube modulator such as the double, triple, etc., frequency components. If, in place of the commutator 30, for example, a vacuum tube Were employed;- assuming the impressed telegraph frequencies comprise components fromzero to cycles, the double frequencies of all. of these compo nents Would be produced with an appreciable amplitude. The transmission range of the filter TF is from 15-0 to 250 cycles and it will be seen that, therefore, the double frequencies of the impressed Waves lying between and 200 cycles would also be transmitted by the filter TF Also in this and the other channels the triple and perhaps higher harmonic frequencies would also appear and be transmitted by the channel filters. The effect of these harmonic frequencies is to distort the transmitted'wave and cause its form to be less'perfect. 'The effect of a d storted wave of this character a similar manner, to produce false signals or at least to give a less definite rectified impulse by which to actuate the receiving relay. Since, however, these harmonic frequencies are not produced by, a commutator the resulting wave term is more accurate and the signals can be reproduced with greater certainty.

ln the case Fig. 1, the main line has been shown as balanced, separate transmitting and receiving commutators for each channel are indicated, and the relays are neutral relays responding to current and nocurrent conditions of the line respectively.

T he invention is equally adapted for use in a system using polarized relays and also there is no ecessity of providing in any case separate transmitting and receiving channels conjugately arranged. In systems using polarized relays it is customary to have current of one polarity normally on the line to indicate a space or non-signaling condition. To signal, this current is replaced by impulses of current of the opposite polarity.

2 and 3 illustrate theinvention as applied to a system using polarized relays. Also the main line is not balanced but each channel contains a single commutating de vice and a band filter or the channel frequencies, these elements serving for both sending and receiving. 7

lt should be noted that the invention secures the same advantages for multiplex carrier operation which a current-reversing system possesses over a current and no-current system in ordinary telegraph operaat the receiver is, in

ion. In the current rever ing system, as usually employed, for a given maxlmuni current flow over the line, the current change is about twice What it would be in a current and no-current system employing the same maximum current flow. If direct current of first one and then the opposite polarity but of the same amplitude is applied to a commutator, a rapidly alt-ernating current is produced having a constant average and also a constant maximum amplitude. However, the elect at the receiver of so reversing the current applied to the commutator is roughly double that of applying impulses oi unidirectional current of the same given strength to the commutatoralternating with intervals of no current.

This will be seen from considerin that the alternating current wave produced from a.

positive impulse immediately following a negative impulse is exactly opposite in phase to the wave produced from the negative impulse. The receiving commutator produces an impulse of one polarity from one such wave. and an impulse of opposite polarity from the other Wave.

' It shoull be noted that a conunutator runn ng insynchrouism with a received alternating can indicated in general at PT rent Wave transmits every other hall wave unchanged and r verses the remaining half waves. The resulting rectified current will then have posi'ive polarity it the commutator transmits s the negative half waves, will he a negative polarity it the nega tive half waves are unchanged but the posi tive reversed. Obviously, a phase shift equal to one half cycle is all the change that is necessary in the line current to change the received rectified current from one polarity to the opposite. This enables a receiving polarized relay to be actuated directly by current reversals derived as directcurrent-impulses of opposite sign from received waves. The current change available for operating thev relay is substantially double the maximum line current. The maximum alternating current amplitude of the line the positive hall waves current remains substantially unsynchronizing,

ln Big. 2., the printing,

carrier and the driving devices for the channel commutator-s correspond to those described in connection with Fig.1 and are The main line Ml terminates in filters HP and LP acting precisely as HP and LP respectively of-Fig. 1 to separate the alternating current channel currents as a whole from the printing telegraph impulses. The filter H1 leads to ti e channel filters El B1 etc., each of uthich serves to transmit to and receive from the line the currents oi the frequencies utilized by its respective channel. These filters are preferably of the form shown at TF, in mutators are run at relatively high frequencies, these filters mightbe replaced by single tuned circuits as might also the filters TF RF, etc., of Fig. 1 under similar conditions; Since all three channels shown are or may be identical except for the rrequencies which they emplo most one in the figure will be described. The commutator 4:5 as here arranged serves to convert direct-current impulses into alternating current for transmission and also to convert received alternating currents into direct-current impulses for signal reception. These two-way operations of the connnutator can take place simultaneously or at different times, as may be desired.

lhe direct current terminating circuit may have any one of several arrangements.

teries 4i? and i8 are arranged to be c'onnect-. ed. under control. o; relay 5O acrossthe line Fig. 1, but if the coin-V only the upperand at a pointbetween the windings of relay 46. Relay 46 is balanced therefore with respect to impulses impressed from 47 or 48 and does not respond thereto. Relay is shown controlled from a transmitting ter-- minal circuit- L" and relay 46 controls a receiving terminal circuit L A polarized sounder 51 is connected in the circuit L The circuits L L may lead as separate lines to any desired distant points, or they may be associated in any of several wellknown manners with an outgoing telegraph line (not shown) for'duplex or half-duplex operation as may be desired. The various elements are shown in their spacing or nonsignaling positions. v

In operation relay 50 in responding to spacing current in the circuit L connects battery 48 to theccircuit 49 and relay 46 remains unresponsive to this current since the current flows equally and in opposite directions through tl e two coils of the relay. This current is transmitted through the filter L1 corresponding to filter LF of Fig. 1, and is applied to the brushes of commutator 45. The action of the commutator is to convertthis current into rapidly alternating current of definite frequency which is transmitted to line through the channel filter BF and the high-pass filter H1 An impulse of signaling polarity in the circuit L causes relay 50 to connect battery 47 in place of battery 48 acrossthe line 49 and current of this changed polarity when applied to commutator 45 is converted into alternating current of similar characteristics to that produced when battery 48 is in circuit except that a phase-inversion takes place when current of one polarity in circuit 49 replaces current of opposite polarity as explained above.

In reception current waves of the frequency employed by the channel being described are received from the line ML through filters HP and BF 1 and applied to the terminals of commutator 45. Since as explained in connection with Fig. 1, this commutator is assumed to be operating in synchronism with the received alternating currents its action is to convert the received currents into direct current, the polarity of which will depend upon whether at the instant when the reversing segments come into functioning the halt-wave being received from the line is positive or negative. This, of course, is controlled at the distant trans mit-ter, and as a result of this control as above explained, the rectified currents will consist of both positive and negative impulses which will actuate relay 46 to control the circuit L The local sounder 51 may be for monitoring purposes.

Instead of the balanced terminal circuit 49 containing network N and balanced relay 46, a simplex circuit as shown in Fig. 3 may under control direct-current impulses.

be employed, the line ab indicating the points ofconnection of this circuit to the line 49. lVith switch 52 in the position shown the polarized relay 53 is in condition to receive impulses of reversing polarity from the distant station. It is assumed in the position shown, to be receiving a marking impulse causing the actuation of sounder 54. To transmit, switch 52 is thrown to its upper'po'sitionand the key is actuated causing reversals ofcurrent from the two batteries shown to be applied to theline of relay 56. The distant operator can send a break signalby moving his switch 52 to its sending position which will have the efiect of reducing the line:

current to zero for certain intervals and preventing relay 53 from following the movements of the sending operators key. This arrangement permits the advantages to be gained resulting from the use of current reversals instead of merely makes and breaks.

In Fig. 1, the rela Y 36 made to control application of current of alternate polarities in the same way as relay 56 of Fig. 3, the relay 53 being omitted from the circuit in such a case. Relay 39 might obviously be and'each of theother receiving relays could then be replaced by a polar relay such as 53 if desired.

It is to be understood that the invention is not limited to the actual circuit arrange ments shown or described but that it is capable of various modifications and its separate featuresare capable of general application Its scope will be defined in the claims.

hat is claimed is: v I

1. The method of telegraphycomprising subdividing direct current telegraph impulses and reversing the alternate subdivided portionsto convert said current impulses into alternating current of definite frequency, transmitting said alternating current and reversing alternate portions of transmitted alternating current at a synchro-v nous rate to reproduce said cu rent impulses.

2. The method of telegraphy comprising subdividing direct current telegraph im: pulses and reversing the alternate subdi vided portions to convert said current impulses into. alternating current of definite frequency, selectively transmitting said al. ternating current to a distance, selectively receiving said alternating current and syn-v chronously reversing the alternate portion of the received current to reproduce said 3. The method of multiplex telegraphy which comprises subdividing a plurality of telegraph direct current impulses represent ing respective messages and reversing the alternate subdivided portions at respectively different rates to produce alternating currents of respectively dillerent frequencies,

simultaneously transmitting the said alternating currents of different frequencies over the same path and selectively receiving the message currents in accordance with the frequencies of the transmitted currents.

t. The method of multiple); telegraphy comprising subdividing each of a plurality of direct-current message currents and reversing the alternate subdivided portions of said currents at respectively different rates and simultaneously selectively transmitting the commutated currents over the same path.

5. The method of multiplex telegraphy which comprises transmitting current impulses representing certain telegraphic messages directly to line, commutating currentimpulses representing other telegraphic messages to convert said impulses into alternating currents of frequencies higher than the frequencies of said on rent impulses, transmitting said alternating: currents v to line, separating said high frequency currents from said transmitted current impulses by filtering, receiving said transmittedimpulses directly from the line and commutating said high frequency currents to convert them into telegraphic current impulses for message reception. V

6. In a telegraph system, a mainline, terminal telegraph circuits carrying, direct current message impulses, and current reversing commutators for converting said direct current message impulses into alternating currents of different frequencies for transmission over said line.

7. In a telegraph system, a main line, terminal telegraph circuits, current reversing commutators connected between said terminal telegraph circuits and. said line, and frequency selective circuits connected between said commutators and. said line.

8. In a telegraph system, a line, means to transmit alternating currents thereover in accordance with telegraph signals, a direct currentiterminal telegraph circuit and a current reversing commutator operated in synclironism with said alternating currents for converting said alternating currents into direct current messageiinpulses and impressing the direct currentiinpulses on said. terminal telegraph. circuit.

9. In a telegraph system, a main line having stations, a direct current. terminal telegraph circuit at each of two stations on. said line, synchronously operating current reversing commutators, one at each of said stations connected between the main line and a said terminal telegraph circuit, one. of said commutators serving to, convert direct current telegraph impulses, into alternating currents for transmission over said line and the. other commutator serving to convert received alternating. currents into. direct current telegraph impulses for the associated terminal circuit. v

10. In a multiplex telegraph system, a

'quencies employed by main line, two or more direct current terminal telegraph circuits at the same terminal of said line, an individual current reversing commutator connected between each terminal circuit and said line for converting direct current telegraph impulses in said terminal circuits into alternating currents for transmission over said line, said commutat'ors each having commutations, whereby the several alternating currents so produced have different frequencies. V

11. In a multiple telegraph system, a main line, means to transmit simultaneous-- ly thereovcr alternating currents of different frequency representing separate messages, t'wo or'niore direct current terminal circuits at the same terminal of said line,

a commutator for each said terminal circuit, 1

each commutator arranged to operate in synchronism with a different one of said alternating current transmissions for converting the corresponding alternating current into direct current impulses for the associated terminal circuit. 7

12'. In a multiplex telegraph system, a main line having stations, a plurality of di rect current terminal telegraph circuits' at each station, a separate commutator between each of the terminal circuits at one station and said line having respectively Cllfifi l'" rent rates of current commutation for con verting the direct current impulses in each a different rate of 7 of the associated terminal telegraph circuitsinto alternating currents of as many different frequencies for transmission over said line, commutators at the other station connected between'said line and the respective terminal telegraph circuits, each one of said last-mentioned cominutators operating in synchronism with a different respective commutator at the first-men tioned station for converting the re ceived'alternating currents of the different frequencies into direct current telegraph impulses for the several associated terminal circuits and tween. each of said commutators and the line. for distinguishing between the fretators.

13. In a multiplex telegraph system, a line, a printing telegraph channel including a rotary distributor, an alternating current,

telegraph channel including a rotating current reversing commutator for converting telegraphic current message impulses into alternating currents. for transmission and a common driving,- means for said rotary tributor and said rotating commutator.

14. In a mult line, means, to transmit telegraphic current impulses thereover, means to transmit also alternatingcurrents thereover having frequencies higher than said'current impulses,

selective circuits connected be the several commu ipleX telegraph system, a-

. the commutator circuit the telegraphic im 7 pulses on said line.

15. A composite telegraph system, comprising a line, a printing telegraph channel arranged to transmit thereover including synchronize-d transmitting and receiving .rotary distributors at respective terminals of said line, and a plurality of carriercurrent channels also arran ed to transmit over said line, each channel including com mutators at each terminal, all of said commutators and said rotary distributors at the same terminal having common driving means.

16. In a telegraph system, a main line for transmitting alternating current telegraph signals, a transmitting and a receiving branch for said line at the same station, a transmi ting direct current terminal cirwit, a receiving direct current terminal circuit, a current reversing commutator connected between the transmitting circuit and the transmitting branch for converting di-' rect current message impulses in said trans mitting terminal circuit into alternating current for transmission over said line and a current reversing commutator connected between said receiving branch and said receiving terminal circuit for converting alternating currents received over said line into direct current for said receiving terminal circuit.

17. A system according to claim 16 having a selective circuit connected between each of said commutators and the respective transmitting or receiving branch of said line.

18. in a carrier telegraph system, a current reversing commutator device for converting the energy or the received carrier waves into direct current energ an out put circuit for said device, a polarized relay having its Winding connectedin the said circuit, said device being arranged to produce direct current flow in either direction through said windings to actuate said relay in the corresponding direction.

19. In a carrier telegraph system, a sending station, a distant receiving station, means at the sending station to produce direct current impulses of opposite polarities, means to transmit the energy of said impulses to the receiving station in the form of carder currentwaves, means at the re ceiving station for converting said carrier current into direct current impulses and a polarized relay arranged to be actuated in opposite directions by the energy of the converted impulses.

1 20. In a carrier telegraph system, a sendingcircrut having means to produce therein, code pulses oi positive and negative can t, a translating circuit for converting sa' impulses into carrier current, a receiv- 1 ing translating circuit for converting said ca 1 current into code impulses and a pcla relay arranged to actuate its armature in opaosite directions in response to said rempulses, the only source of current employed being in said sending circuit.

in a multiplex carrier telegraph system, a line having stations, a plurality of selective circuits for passing each a diilerent frequency connected to said line at the same station, a current reversing commutator connccted to each selective circuit on the opposite side from said line connection, said cominu'tators being arranged to have respective rates oi current alt rnation Within the transmission range of the associated selective cir telegraph circuits concuit and terminal nected to said commutatcrs.

A two-way translating circuit for carrier telegraph line comprising a selective circuit ior receiving alternating current iron'i the line and transmitting alternating cuJrentto the ins, a direct current telegraph circuit, and a commutator connected between saidtelegraph circuit and said se lective circuit for converting direct current telegraph impulses into alternating current for the line and alternating current received from the line into direct current telegraph impulses.

two-way carrier telegraph channel comprising at each of two stations a single current reversing commutator, said commutators'operating in synchronism and each serving to convert direct current telegraph impulses into alternating current and alternating current into direct current.

A two-Way trans ating device-for an alternating or carrier current.chanuel for converting direct current telegraph impulses into carrier current impulses and carrier current impulses into direct current impulses comprising a current re 'ersing commutator operating in synchronism with the carrier current alternations.

In a carrier telegraphsystem, a current reversing commutator running at a definite ccmmutating frequency, a direct current telegraph circuit, sources of current of opposite polarities in said circuit, a high frequency line, said commutator arranged to convert message current of each polarity in said telegraph circuitiuto alternating current for transmission over said high fr from said telegraph circuit on to said commutator to produce alternating current for transmission over said line, and means to impress on said commutator alternating currents received from .said line to produce direct current message impulses for transmission over said telegraph circuit.

2?. A two-Way repeating circuit for use between a direct current line and a high frequency line, comprising a current reversing commutator arranged to convert direct current telegraph impulses into alternating current telegraph impulses and alternating current telegraph impulses into direct current telegraph impulses.

28. In a carrier telegraph system, means comprising a currcnt-reversing commutator to-convert energy of direct current telegraph impulses into the energy of alternating current and means comprising a GLlYTGllliilQVElS' ing commutator to reconyert said energy of alternating current into directcurrent telegraph impulses.

29. In a carrier telegraph system, means comprising a current-reversing comn'rutator to convert energy of direct current telegraph impulses of one polarity into the en ergy of alternating current, and to convert the energy of direct curr-ent'telegra nimrent energy of one polarity and't'o' reconver't' said alternating current energyor" opposite phase into directcu'rrent energyofopposite polarity from said last mentioned direct current energy.

30. The method of t'e'legraphy comprising subdividingdirect CUIIEflii telegraph ini pulses of respectively opposite polarityand reversing the alternate subdivided portions to produce aiterna-tmg' currents of respectiteljj opposite phase, and a receiving point reversing alternate portions of said alternating currents to reconvert said alternating currents of resp'ectit-"elyopposite phase into" direct current impulses of respectively opposite polarity;

In Witness whereof, I hereunto subscribe my nametliis 28th--day of February A. 1);, 1922.

RALPH v. L. HARTLEY. 

